Americans who live in areas with high concentration of ozone are at greater risk for decreased lung function, respiratory infection, lung inflammation and aggravation of respiratory illness, the report said.

Increased particle pollution -- dust, ash and soot combined with chemical aerosols -- can lead to greater risk of heart attacks and strokes while chronic exposure could mean more risk of hospitalization for illnesses including asthma.

``We have a very long way to go before we can declare we have cleaned up the air,'' Frank O'Donnell, president of the environmental group Clean Air Watch, said in an e-mail yesterday. ``So much attention has been given to global warming that sometimes we forget there are other serious problems caused by emissions from smokestacks and tailpipes.''

O'Donnell called the report a ``sobering snapshot'' of air in the U.S.

Ozone forms at ground level when hydrocarbons and nitrogen oxides, mainly from power plants, factories and car exhaust emissions, react to sunlight, according to the American Lung Association.

The Environmental Protection Agency announced new national rules March 11 that will require cities and communities to set policies to reduce ground-level ozone, or smog, the first tightening of air-quality standards since 1997 to reduce pollution from factories, automobiles and utilities.

Older Standard Used

The regulations allow no more than 75 parts of ozone for every billion parts of air, down from 85 parts-per-billion.

Today's study reflects the EPA's older ozone requirements because there wasn't enough lead time to re-calculate the grades, Janice Nolen, lung association assistant vice president for national policy and advocacy, said in an April 29 conference call with reporters previewing the report's findings.

``If we had used the tighter standard, the grades would have been worse,'' Nolen said.

The Bush administration has been under court order to update the air standards after settling a 2003 lawsuit brought by the American Lung Association.

Cathy Milbourn, an EPA spokeswoman, said the agency will review the report, and officials believe ``the nation's air quality is getting cleaner.''

Supreme Court Decision

The Supreme Court, in a 5-4 decision a year ago, ruled that the EPA failed to follow the requirements of the Clean Air Act in 2003 when it opted not to order cuts in carbon emissions from new cars and trucks. The court said the agency couldn't refuse to exercise its authority based on policy preferences and has to act on scientific determinations.

``What's clear is that Americans are still being denied the health protection they deserve under the Clean Air Act,'' Bernadette Toomey, president of the lung association, said in the April 29 conference call with reporters.

The study recommends strengthening the country's Clean Air Act and cleaning coal-fired power plants as well as existing diesel equipment.

A city outside of California topped one of the most polluted lists for the first time in the study's nine-year history. Pittsburgh is the country's most polluted city in short-term particle pollution, the report found.

Los Angeles, which topped the two most polluted lists for ozone and year-round particle pollution, has seen improvements in air quality over the last decade.

Control Monitors

Today's study grades the air quality in more than 700 of more than 3,000 counties in the U.S. for 2004 to 2006, the most recent quality-assured data.

The surveyed counties were chosen because each has air pollution control monitors, Nolen said.

The top 10 most ozone-polluted cities are Los Angeles-Long Beach-Riverside, California; Bakersfield, California; Visalia/Porterville, California; Houston, Texas; Fresno-Madera, California; Sacramento, California; Dallas-Fort Worth, Texas; New York, New York-Newark, New Jersey; Baltimore, Maryland- Washington, DC-northern Virginia; and Baton Rouge, Louisiana.

To contact the reporter on this story: Nadine Elsibai in Washington at nelsibai@bloomberg.net.

Last Updated: May 1, 2008 17:08 EDT

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